1. Field of the Invention
The present invention relates to a facsimile communication control system in a mobile communication system that includes: a mobile station composed of a mobile unit for controlling radio lines for mobile communication, a facsimile device that can transmit and receive facsimile signals, and an adapter that connects the mobile unit and facsimile device; a mobile communication exchange that accommodates this mobile station by way of radio lines; and a supplementary exchange device connected to this mobile communication exchange that controls facsimile communication through a prescribed protocol according to facsimile communication process requests from the mobile station.
2. Description of the Related Art
FIG. 1 is a block diagram showing a typical mobile communication system that performs facsimile communication. FIG. 1 presents a case in which the facsimile devices of each of two mobile units connected by way of a mobile communication network are connected and facsimile communication is performed reciprocally between the two facsimile devices, but a case may also be considered similarly in which a mobile communication network is used on only the transmitting side or receiving side.
Mobile station 1 (2) is composed of mobile unit 13 (23) that controls radio lines for mobile communication; facsimile device 11 (21) capable of transmitting and receiving facsimile data; and mobile unit-facsimile connection adapter (hereinbelow referred to as "connection adapter") 12 (22) for connecting facsimile device 11 (21) to mobile unit 13 (23).
Radio base stations 35 and 36, which control radio lines for mobile unit communication, are controlled by mobile communication radio line control stations 33 and 34, respectively. Mobile communication exchanges 31 and 32 are connected to each other by way of inter-station line 43, and in addition, accommodate mobile stations 1 and 2 by way of mobile communication radio line control stations 33 and 34 and radio base stations 35 and 36, respectively, and switch/connect mobile communication calls to mobile stations 1 and 2. Supplementary exchange devices 37 and 38 are connected to mobile communication exchanges 31 and 32, respectively, and control facsimile communication based on a prescribed transmission control protocol in response to initiation at the time of facsimile communication. Radio lines 41 and 42 connect radio base stations 35 and 36 to mobile units 13 and 23, respectively.
Operation of a prior-art mobile communication system will next be explained with reference to FIG. 2. FIG. 2 is a sequence chart from the midpoint to the end of a facsimile transmission from facsimile device 11 to facsimile device 21 between mobile stations. This sequence is a protocol proposed by Standard RCR-STD27C of the Research and Development Center for Radio Systems (RCR) and is based on call control protocol for facsimile communication employing facsimile devices in mobile communication.
Facsimile device 11, which has at this point completed transmission of image signal Pix, sends DCN indicating completion of facsimile communication to connection adapter 12, thus completing facsimile transmission by facsimile device 11. After completing transmission of Pix to supplementary exchange device 37, connection adapter 12, which has received DCN, sends DCN to supplementary exchange device 37, and executes an OFF request to mobile unit 13. After receiving DCN, supplementary exchange device 37 completes transmission of Pix to supplementary exchange device 38, following which it sends DCN to supplementary exchange device 38.
Supplementary exchange device 38, having received DCN from supplementary exchange device 37, completes transmitting Pix to connection adapter 22 and then sends DCN to connection adapter 22. Connection adapter 22 having received DCN, completes sending Pix to facsimile device 21 and then sends DCN to facsimile device 21 and executes an OFF request to mobile unit 23, thereby completing facsimile reception by facsimile device 21.
Mobile unit 13, having received the OFF request, sends INFO indicating non-speech completion to mobile communication exchange 31. Mobile communication exchange 31, having received this INFO, transmits INFO indicating current inactivity to mobile unit 13, and mobile unit 13 and mobile communication exchange 31 resume conversation.
DISC, which is a call-disconnect signal, is then sent by mobile unit 13 to mobile communication exchange 31, following which mobile communication exchange 31 both sends DISC to mobile communication exchange 32 and sends REL indicating the release of the telephone call to mobile unit 13, and when RELCOM indicating completion of release of the telephone call from mobile unit 13 to mobile communication exchange 31 has been transmitted, the telephone call between mobile unit 13 and mobile communication exchange 31 is released.
Mobile communication exchange 32, having received DISC from mobile communication exchange 31, sends DISC to mobile unit 23. Mobile unit 23 transmits REL, and when RELCOM is transmitted from mobile unit 13 to mobile communication exchange 31, the telephone call between mobile unit 13 and mobile communication exchange 31 is released.
The facsimile communication from facsimile device 11 to facsimile device 21 is thus completed.
In the above-described mobile communication system, the problem occasionally occurs that, if the transmitting-side facsimile device terminates facsimile transmission when Pix reception at the receiving-side facsimile device is delayed due to some reason such as poor line quality, the telephone call is discontinued midway even though the receiving-side facsimile device is still in the process of receiving, thereby disrupting the facsimile communication process at the end of the facsimile communication.
The reason for this problem can be explained by means of the example shown in FIG. 3.
As in FIG. 2, this figure shows a sequence chart from the midpoint to completion of facsimile communication between mobile stations from facsimile device 11 to facsimile device 21, the transmission procedure on the transmitting side being the same as in FIG. 2.
In this case, when the transmission of Pix between supplementary exchange device 38 and connection adapter 22 is delayed for some reason, mobile communication exchange 32 receives DISC from mobile communication exchange 31 during Pix transmission, whereupon mobile communication exchange 32 sends DISC to mobile unit 23, and, having received DISC, mobile unit 23 sends REL to mobile communication exchange 32 and facsimile communication is terminated midway by turning connection adapter 22 OFF.